The present invention relates broadly to a container having an inner surface of a blend of polybutylene terephthalate and polyethylene. The invention is more particularly concerned with a dispensing container of a multilayer construction the innermost layers being a blend of polybutylene terephthalate and polyethylene whereby product permeation and absorption, and oxygen absorption, are substantially prevented in the regions of the container with this structure.
Tubes formed of metallic and plastic materials have long been known in the packaging field. Extruded metal tubes are inherently brittle and repeated use not infrequently results in wall cracks so that product is exuded from a location other than the essentially rigid dispensing orifice. Of the prior art metal tubes, aluminum tubes, while probably being the least brittle, are somewhat limited in their applications since up to the present time it has not been possible to apply to the interior surfaces thereof a completely satisfactory coating. A coating is required to prevent attack and corrosion of the metal by alkaline or acid contents and contamination of the contents by the reaction products. Notwithstanding the relatively brittle nature of a metal tube, the mentioned internal coating operation requires an additional processing step which necessarily increases the cost of the final article.
Tubes formed of polyethylene and other plastic materials have enjoyed wide commercial success in the packaging of many products. These are both singe layer and multi-layer tubes. However, certain products after a time have been noted to deteriorate when contained in polyethylene. Plastics as exemplified by polyethylene are to a degree permeable to organics when employed in the relatively low wall thicknesses used in tubular containers. This results in the flavor oils embodied in most dentifrices being reduced in volume during rendering the dentifrice less palatable.
One solution has been proposed to provide a relatively thin metallic foil barrier between the product and the polyethylene tube body to prevent the mentioned loss of essential oils and the absorption of oxygen. The metallic barrier has been suggested as an interlayer between facing sheets of polyethylene, and the laminate be formed by heat with or without suitable adhesives. However, while a structure of this general character is effective to prevent some product permeation and oxygen absorption through the tube body, the tube must be of a laminate construction. It cannot be extruded or blow molded.
U.S. Pat. No. 4,243,712 discloses the use of plastic tubes made from polyethylene terephthalate. This is stated to be a flavor barrier. However, the main use for the tubes is as a shrink film. There is no disclosure to use of this film with pastes. Further, there is no disclosure of the use of this film to make tubes to hold and dispense dentifrices. In addition, there is no disclosure to use a blend of polybutylene terephthalate and polyethylene.
U.S. Pat. No. 4,327,726 also discloses a tube comprised of polyethylene terephthalate. This is similar to a related disclosure in U.S. Pat. No. 4,009,734. In each instance, the polyethylene terephthalate tube is used as a conduit means. It is not used to contain a dentifrice or a related flavored substance. Further, there is no disclosure in these patents to use a blend of polybutylene terephthalate and polyethylene. In particular, there is no disclosure with regard to the synergism when a blend of polybutylene terephthalate and polyethylene is used. The flavor oil absorption by the blend is less than when either polyethylene or polybutylene terephthalate is used alone.
U.S. Pat. No. 3,295,725 discloses a laminated collapsible dispensing container. This container has a metallic barrier and a polyethylene inner wall. The laminates that are disclosed in this patent make acceptable dispensing tubes, however, these dispensing tubes suffer from a high absorption of flavorant oils. This is illustrative of the prior art problem.
U.S. Pat. No. 4,595,612 discloses the structure of a toothpaste dispensing tube which has as the inner layer a layer of polyethylene terephthalate. This polyester produces a good tube laminate and absorbs less flavor oil than a polyethylene barrier layer. However, there is not disclosed the use of polybutylene terephthalate nor the use of a polybutylene terephthalate polyethylene blend as the structural layer for a toothpaste dispenser that is in contact with the paste.
Canadian Patent 728,525 discloses the use of a metal layer coated with polyethylene for use in making dentifrice dispensing tubes. However, as has been pointed out polyethylene will absorb a large amount of the flavorant oils in a dentifrice composition. This patent also illustrates the prior art problem.
A further disadvantage in a polyethylene surface resides in the inability of the surface to readily receive printing or decorative material. In addition, polyethylene has a memory property, that is, it does not remain compressed when squeezed. This is a disadvantage for some dentifrice tubes. To counter such a lack of deformability the metal layer must be relatively thick so that deformability is imposed on the plastic so as to overcome its memory.
All of this can be overcome through the use of a blend of polyethylene and polybutylene terephthalate. Such a blend has properties superior to those of polyethylene alone or polybutylene terephthalate alone. The blend exhibits a synergism with regard to a significant decrease in the degree of absorption of flavorants from liquids and pastes and is more readily suitable.